Zinc acid bath electroplating

ABSTRACT

NOVEL ACID AQUEOUS ELECTROPLATING BATHS FOR FORMING LUSTROUS ZINC DEPOSITS CONTAINING A WATER-SOLUBLE ZINC SALT, USUAL LUSTERING AGENTS AND WETTING AGENTS, OPTIONALLY AN ADDITIONAL CONDUCTING SALT AND A THIOUREA DERIVATIVES OF THE FORMULA   R-NH-C(=S)-N(-R1)-R2   WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF ALKYL OF 6 TO 22 CARBON ATOMS, A MONO- OR POLYNUCLEAR ARYL WHICH MAY OPTIONALLY BE SUBSTITUTED WITH AN ALIPHATIC OR AROMATIC GROUP, ARYLALKYL AND CYCLOALKYL, R2 IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN AND HYDROXYALKYL OF 2 TO 6 CARBON ATOMS WHICH MAY OPTIONALLY BE INTERRUPTED BY AN ETHER OXYGEN AND R2 IS HYDROXYALKY OF 2 TO 6 CARBON ATOMS WHICH MAY BE OPTIONALLY INTERRUPTED BY AN ETHER OXYGEN AND TO A NOVEL ELECTROPLATING METHOD FOR FORMING LUSTROUS ZINC DEPOSITS AND ZINC DEPOSITS FORMED BY SAID METHOD.

United States Patent Ofice US. Cl. 204-55 R 7 Claims ABSTRACT OF THE DISCLOSURE Novel acid aqueous electroplating baths for forming lustrous Zinc deposits containing a water-soluble Zinc salt, usual lustering agents and wetting agents, optionally an additional conducting salt and a thiourea derivative of the formula S R; RNH(|N/ R2 (1) wherein R is selected from the group consisting of alkyl of 6 to 22 carbon atoms, a monoor polynuclear aryl which may optionally be substituted with an aliphatic or aromatic group, arylalkyl and cycloalkyl, R is selected from the group consisting of hydrogen and hydroxyalkyl of 2 to 6 carbon atoms which may optionally be interrupted by an ether oxygen and R is hydroxyalkyl of 2 to 6 carbon atoms which may be optionally interrupted by an ether oxygen and to a novel electroplating method for forming lustrous zinc deposits and zinc deposits formed by said method.

STATE OF THE ART Most of the commercial zinc electroplating baths for forming lustrous zinc deposits operate with an alkaline bath and the most widely used alkaline electroplating baths are the cyanide lustrous zinc baths. However, the detoxification of the waste water resulting from these electroplating baths causes an economical problem which results in criticism of these baths and various attempts have been made to replace cyanide lustrous zinc baths with other types of baths.

These attempts have included cyanide-free alkaline zinc baths and also acid Zinc baths in which the waste water can be disposed of without difficulty and without great expense. In spite of the advantage of simple disposal of waste water, the acid zinc baths of the prior art have a number of disadvantages which make them unsuitable for extensive industrial use.

In some baths, the zinc deposits are dull, and when one succeeds in imparting luster to the deposits, their depth dispersion still leaves much to be desired and the current density range in which lustrous deposits are obtained is within very narrow limits. Apart from this, the

* deposits obtained frequently show a great embnttlement. In spite of all eliorts, an effective prevention of all the disadvantages at the same time has not been found and only limited and partial improvements have been obtained, which often result in intensifying another disadvantage. Therefore, until now there has been no acid lustrous zinc bath which provides over a wide range of current densities embrittlement-free deposits of good lustre with good depth dispersion.

OBJECTS OF THE INVENTION It is an object of the invention to provide novel aqueous acid electroplating baths for forming lustrous zinc deposits.

3,700,570 Patented Oct. 24, 1972 It is another object of the invention to provide a novel method of forming lustrous zinc deposits over a wide range of current densities.

These and other objects and advantages of the invention will become obvious from the following detailed description.

THE INVENTION The novel aqueous acid electroplatic baths of the invention contain a water-soluble zinc salt, usual lustering agents and wetting agents, optionally an additional con: ducting salt and a thiourea derivative of the formula R: (I) wherein R is selected from the group consisting of alkyl of 6 to 22 carbon atoms, a monoor polynuclear aryl which may optionally be substituted with an aliphatic or aromatic group, arylalkyl and cycloalkyl, R is selected from the group consisting of hydrogen and hydroxyalkyl of 2 to 6 carbon atoms which may optionally be interrupted by an ether oxygen and R is hydroxyalkyl of 2 to 6 carbon atoms which may be optionally interrupted by an ether oxygen.

Preferably, R is alkyl of 6 to 22 carbon atoms, phenyl or naphthyl which may be further substituted with alkyl of l to 10 carbon atoms such as methyl or nonyl, halogens such as chlorine or bromine, sulfonyl or phenyl, cycloalkyl of 5 to 12 carbon atoms such as cyclopentyl, cyclohexyl, menthyl or bornyl and phenyl lower alkyl such as benzyl or phenethyl.

Examples of suitable compounds of Formula I are N-hexyl-N b -hydroxyethoxy)-ethyl, N-octyl-N'- ('y-hydroxyethoxy) -propyl-, N-dodecyl-N- ('y-hydroxyethoxy -ethyl-, N-octadecyl-N'- ('y-hydroxyethoxy) -ethyl-, N-phenyl-N'- ('y-hydroxyethoxy -ethyl-, N-diphenyl-N- ('y-hydroxyethoxy) -propyl-, N-a-naphthyl-N'-('y-hydroxyethoxy)-ethyl-, N-tosyl-N- -hydroxyethoxy -propyl-, N-nonylphenyl-N 'y-hydroxyethoxy) -ethyl-, N-benzyl-N'- ('y-hydroxyethoxy) -ethyl-, N-cyclopentyl-N- 'y-hydroxyethoxy -propyl-, N-cyclohexyl-N- (y-hydroxyethoxy) -ethyl-, N-p-menthyl-N'd 'y-hydroxyethoxy -ethyl-, N-bornyl-N 'y-hydroxyethoxy pro pyl-, N-phenyl-N'- ('y-hydroxyethoxy -isopropyl-N- octyl-N'-'y-hydroxyethyb, and N-benzyl-N-bis'- -hydroxyethyl) -thiourea.

The thioureas of Formula I can be prepared by known methods by .reacting a mustard oil of the formula R--NCS with an amine of the formula wherein R, R and R have the above definitions or by reacting a thiourea of the formula R-NHCS-NH with a lower alkylene oxide such as ethylene oxide, propylene oxide or butylene oxide.

The concentration of the thiourea derivatives of Formula I in the zinc electroplating baths may be between 0.01 to 10 gm. per liter, preferably between 0.1 to 5.0 gm. per liter, of bath liquid. The current density used for the electroplating method is between 0.5 to 8 a./dm. at a bath operating temperature of 10 to 40 C. preferably 15 to 30 C. The pH of the acid baths is generally in the range of 3 to 5.

The water soluble zinc salt may be any of the usual zinc salts such as zinc chloride or zinc sulfate or mixtures thereof. Preferably, the acid baths contain 25 to 450 gm. per liter of bath liquid of the zinc salt. The additional conducting salt which may be present in the bath is preferably a water soluble aluminum salt such as its chloride or sulfate. The amount of said additional conducting salt is 1 to 50 gm. per liter of bath liquid.

Various wetting agents can be added to the acid baths in amounts of 0.5 to gm. per liter of bath liquid. Especially preferred for use in an acid zinc chloride bath are non-ionic melting agents by the adducts of an alkylene oxide such as ethylene oxide and/ or propylene oxide and high molecular weight aliphatic alcohols or alkyl phenols such as the adducts of 2 to 100 moles of ethylene oxide and 1 mole of a straight or branched chain aliphatic alcohol of 8 to 22 carbon atoms and mixtures thereof or to alkylphenols such as nonlyphenol. In acid zinc sulfate baths, the wetting agents are preferably anionic compounds such as fatty alcohol sulfates or fatty alcohol ether sulfates or non-ionic compounds of the polyalkylene glycol type. Examples of suitable additives of these types are sulfates or ether sulfates of fatty alcohols of 8 to 18 carbon atoms and polyethylene glycols and polypropylene glycols with a molecular weight of 200 to 600.

Examples of suitable lustering agents are N-phenyl-N'- ('y-hydroxyethyl) 'ethyl-thiourea, N-benzyl-N'- ('y-hydroxyethyl ethyl-thiourea, N-octyl-N- 'y-hydroxyethoxy) -propyl-thiourea, N-a-naphthyl-N- -hydroxyethoxy) ethyl-thiourea, N-cyclohexyl-N'- ('y-hydroxyethoxy) -propylthiourea, N-benzyl-N'-bis- ('y-hydroxyethyl) -thiourea.

In the following examples there are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

EXAMPLE I An aqueous zinc electroplating bath was prepared with the following composition: 110 gm./liter of crystalline zinc chloride (ZnCl -6H O), 175 gm./liter of ammonium chloride, 0.5 gm./liter of N phenyl N ('y hydroxyethyl)-ethyl-thiourea and 5 gm./liter of the adduct of 17 moles of ethylene oxide and 1 mole of isononyl alcohol. The bath had a pH of 4.6. The electroplating bath provided lustrous, ductile zinc deposits with a good covering power at an operating temperature of to 30 C. over a current density range of 2 to 5 a./dm.

EXAMPLE II An aqueous zinc electroplating bath containing 100 gm./liter of crystalline zinc chloride (ZnCl -6H O), 50 gm./liter of crystalline aluminum chloride (AlCl 6H O) 150 gm./liter of ammonium chloride, 2 gm./liter of N benzyl N ('y hydroxyethyDethyl thiourea and 4 gm./liter of the adduct of moles of ethylene oxide and one mole of nonylphenol with a pH of 3 was operated at temperatures of 15 to 30 C. over a current density range of 0.5 to 5.0 a./dn'i. and provided bright to lustrous ductile zinc deposits with a good covering power.

EXAMPLE III An aqueous zinc bath containing 400 g./liter of crystalline zinc sulfate (ZnSO -7H O), 15 g./liter of ammonium chloride, 30 g./liter of boric acid, 0.7 g./liter of N octyl N ('y hydroxyethoxy) propyl-thiourea and 5 g./liter of sodium salt of the C C -fatty alcohol sulfate and having a pH of 3.5 was operated at a temperature of 15 to 30 C. over a current density range of 4 0.5 to 3 a./dm. to obtain bright, ductile zinc coatings with satisfactory covering power.

EXAMPLE IV An aqueous zinc bath containing 240 g./ liter of crystalline zinc sulfate (ZnSO -7H O), 30 g./ liter of crystalline aluminum sulfate (Al (SO -l8H O), 15 g./liter of sodium acetate, 0.2 g./ liter of Not-naphthyl-N'-('y-hydroxyethoxy)-ethyl-thiourea and 4 g./ liter of sodium salt of the C -C -fatty alcohol sulfate and having a pH of 4.0 was operated at a temperature of 15 to 30 C. over a current density range of 0.5 to 5 a./drn. to provide bright, ductile zinc coatings with excellent covering power.

EXAMPLE V An aqueous zinc bath containing 400 g./ liter of crystalline zinc sulfate (ZnSO -7H O), 1S g./liter of ammonium chloride, 30 g./liter of boric acid, 1 g./liter of N-cyclohexyl-N'-('whydroxyethoxy)-propyl-thiourea, 5 g./liter of sodium lauryl ether sulfate having a pH of 3.5 was operated at a temperature of 15 to 30 C. over a current density range of 0.5 to 5 a./dm. to obtain lustrous, ductile zinc coatings with satisfactory covering power.

EXAMPLE VI An aqueous zinc bath containing 240 g./ liter of crystalline zinc sulfate ZnSO -7H O, 30 g./liter of crystalline aluminium sulfate [Al (SO -l8H O], 15 g./liter of sodium acetate, 1 g./liter of 'N-benzyl-N-bis-(' -hydroxyethyl) thiourea and 5 g./liter of sodium lauryl ether sulfate having a pH of 4.0 was operated at a temperature of 15 to 30 C. over a current density range of 0.5 to 5 a./dm. to provide bright, ductile zinc coatings with satisfactory covering power.

Various modifications of the bath and process of the invention may be made without departing from the spirit or scope thereof and it should be understood that the invention is to be limited only as defined in the appended claims.

I claim:

1. In an acid aqueous electroplating bath for forming lustrous zinc deposits comprising a bath containing a water-soluble zinc salt, usual lustering agents and wetting agents and optionally an additional conducting salt, the improvement comprising incorporating in the bath from about 0.01 g./l. to about 10 g./l. of a thiourea derivative of the formula wherein R is selected from the group consisting of alkyl of 6 to 22 carbon atoms, phenyl and naphthyl optionally substituted with at least one member of the group consisting of alkyl of 1 to 10 carbon atoms, halogen, sulfonyl and phenyl, cycloalkyl of 5 to 12 carbon atoms and phenyl lower alkyl, R is selected from the group consisting of hydrogen and hydroxyalkyl of 2 to 6 carbon atoms which may optionally be interrupted by an ether oxygen and R is hydroxyalkyl of 2 to 6 carbon atoms which may be optionally interrupted by an ether oxygen.

2. The bath of claim 1 wherein the amount of thiourea is 0.1 to 5 gm. per liter.

3. The bath of claim 1 wherein the zinc salt is zinc chloride and the bath further contains a wetting agent selected from the group consisting of adducts of ethylene oxide with an alkyl phenol and adducts of ethylene oxide with aliphatic alcohol of 8 to 22 carbon atoms.

4. The bath of claim 1 wherein the zinc salt is zinc sulfate and the bath further contains a wetting agent selected from the group consisting of fatty alcohol sulfates, fatty alcohol ether sulfates and polyalkylene glycols.

5. A method of forming lustrous zinc deposits which comprises passing an electric current at a current density of 0.5 to 8.0 a/dm. through an electroplating bath of 3,203,878 8/1965 Willmund 2045 2 claim 1 operating at a temperature of 10 to C. 3,257,294 6/ 1966 Michael 204 is t'gh; method of claim 5 wherein the pH of the bath FOREIGN PATENTS 7. The method of claim 5 wherein the operating tern- 5 1,547,678 11/1968 France 204 perature is 15 to 30 1,149,106 4/1969 Great Britain 20455 R References Cited F. C. EDMUNDSON, Primary Examiner UNITED STATES PATENTS 10 us. CL XIR. 1,903,860 4/1933 Gockel 20455 RX 204DIG. 2

2,828,252 3/1958 Fischer 20449 

